Electrochemical Immunoassay of Escherichia coli O157:H7 Using Ag@SiO2 Nanoparticles as Labels.

Silica coated silver (Ag@SiO2) nanoparticles were prepared and characterized by transmission electron microscope (TEM) and UV-vis absorption, and the nanoparticles were used as labels in sandwich-type immunosensor of Escherichia coli O157:H7 (E. coli O157:H7). The labels involved in immunoreaction were dissolved by mixed acid of hydrofluoric acid and nitric acid, and the released Ag(+) ions were electrochemical stripping analyzed (via differential pulse voltammetry, DPV) at poly(acrylic acid)/poly(diallyldimethylammonium chloride)/carbon nanotubes (PAA/PDCNT) modified glass carbon electrode (GCE), which obviously enhanced the signal of Ag(+) stripping. Then, the number of E. coli O157:H7 could be indirectly reflected by the signal intensity of labeled Ag(+). And the results showed that the DPV signals were proportional to the logarithm of the E. coli O157:H7 concentration in the range from 20 cfu/mL to 8.0 × 10(3) cfu/mL with the detection limit of 13 cfu/mL.